如何在函数中显示结构数组

Question

这个程序本质上应该计算随机掷骰子 100 次的结果，并计算每个面的出现次数，然后将它们全部显示为星号的直方图。似乎这些功能可以正常工作，但我无法验证，因为在我做出选择后，什么都没有显示。

#include <iostream>
#include <iomanip>
#include <string>
#include <random>
#include <sstream>
using namespace std;


enum class Side {
  ONE, TWO, THREE, FOUR, FIVE, SIX
};

struct Bar {
  int value;
  Side label;
};


//roll dice function
void rollDice( Bar h[], int n = 100);

void rollDice( Bar h[], int){

default_random_engine en;
uniform_int_distribution<> dist{1,6};

    int results[] ={0,0};

    for( int n; n<=100; n++){
        cout << dist(en);
        results[dist(en)]++;
      h[n].value = results[n];        

      if(h[n].value == 1){
          h[n].label =  Side::ONE;
      }
      else if(h[n].value == 2){
        h[n].label =  Side::TWO;
      }
       else if(h[n].value == 3){
        h[n].label =  Side::THREE;
      }
       else if(h[n].value == 4){
        h[n].label =  Side::FOUR;
      }
       else if(h[n].value == 5){
        h[n].label =  Side::FIVE;
      }
       else {
        h[n].label =  Side::SIX;
      }


    }


};

string getHistogram(Bar h[], char c = '*');

string getHistogram(Bar h[], char c ){

stringstream ast;

    for( int n; n<=100; n++){


          switch (h[n].label)
          {
          case Side::ONE:
              return to_string(c);
            break;
          case Side::TWO:
              return to_string(c);
            break;
          case Side::THREE:
            return to_string(c);
            break;
          case Side::FOUR:
            return to_string(c);
            break;
          case Side::FIVE:
            return to_string(c);
            break;  
          case Side::SIX:
            return to_string(c);
            break;  

          default:
            break;
          }
    }

ast << "One: " << c << endl;
ast << "Two: " << c << endl;
ast << "Three: " << c << endl;
ast << "Four: " << c << endl;
ast << "Five: " << c << endl;
ast << "Six: " << c << endl;

string output = ast.str();

cout<< output;
return output;
}


int main (){

Bar histogram[] = {
  {0,Side::ONE},{0,Side::TWO}, {0,Side::THREE},
  {0,Side::FOUR},{0,Side::FIVE}, {0,Side::SIX}

};

char choice;

do {
  cout << "DICE ROLLING SIMULATION" << endl
       <<"===============================" << endl
       << "r. Roll Dice" << endl
       << "h. Display histogram" << endl
       << "q. Quit program\n" << endl

       << "\nEnter your choice:" << endl;

  // Reading a single character using the scanner
  cin >> choice;



  switch(choice) {
  case 'r': case 'R':
     rollDice(histogram, 100);
    break;
  case 'h': case 'H':
    cout<< getHistogram(histogram, '*');
    break;
  case 'q': case 'Q':
    cout << "Good bye\n" << endl;
    break;
  default:
    cout << "Invalid choice\n" << endl;
  }
} while(choice != 'q');

}

Answer 1

所以，这段代码包含许多不同的错误。我们按顺序走吧。

• 在 structBar 标签可能是 const

struct Bar {
  int value;
  const Side label;
};

• 函数签名不需要前向声明
• 在rollDice 中有许多不必要的局部变量，我会使用mt19937 随机生成器。所以rollDice 会是这样的

void rollDice(Bar h[], int count = 100) {
  default_random_engine en;
  uniform_int_distribution<> dist{1,6};

  for( int n = 0; n <= count; n++) {
    cout << dist(en) << endl;
    const auto index = dist(en) - 1;
    ++h[index].value;
  }
};

• 在getHistogram 你有return to_string(c); 在开关因此你看不到直方图。你可以删除swith，因为你可以匹配索引和Side。为什么要循环多达 100 个？

string getHistogram(Bar h[], char c = '*') {
  stringstream ast;
  for( int n = 0; n <= 5; n++) {
    const string strValue = string(h[n].value, c);

    switch (h[n].label)
    {
    case Side::ONE:   ast << "One:   "; break;
    case Side::TWO:   ast << "Two:   "; break;
    case Side::THREE: ast << "Three: "; break;
    case Side::FOUR:  ast << "Four:  "; break;
    case Side::FIVE:  ast << "Five:  "; break;
    case Side::SIX:   ast << "Six:   "; break;
    }

     ast << strValue << '(' << h[n].value << ')' << endl;
  }

  return ast.str();
}

• 在main 函数中，您必须在下一个rollDice 之前清除直方图

case 'r': case 'R':
      for (Bar& b : histogram) {
        b.value = 0;
      }
      rollDice(histogram, 100);
      break;

完整版

#include <iostream>
#include <iomanip>
#include <string>
#include <random>
#include <sstream>
using namespace std;

enum class Side {
  ONE, TWO, THREE, FOUR, FIVE, SIX
};

struct Bar {
  int value;
  Side label;
};

void rollDice(Bar h[], int count = 100) {
  default_random_engine en;
  uniform_int_distribution<> dist{1,6};

  for( int n = 0; n <= count; n++) {
    cout << dist(en) << endl;
    const auto index = dist(en) - 1;
    ++h[index].value;
  }
};

string getHistogram(Bar h[], char c = '*') {
  stringstream ast;
  for( int n = 0; n <= 5; n++) {
    const string strValue = string(h[n].value, c);

    switch (h[n].label)
    {
    case Side::ONE:   ast << "One:   "; break;
    case Side::TWO:   ast << "Two:   "; break;
    case Side::THREE: ast << "Three: "; break;
    case Side::FOUR:  ast << "Four:  "; break;
    case Side::FIVE:  ast << "Five:  "; break;
    case Side::SIX:   ast << "Six:   "; break;
    }

     ast << strValue << '(' << h[n].value << ')' << endl;
  }

  return ast.str();
}


int main (){
  Bar histogram[] = {
    {0, Side::ONE},
    {0, Side::TWO},
    {0, Side::THREE},
    {0, Side::FOUR},
    {0, Side::FIVE},
    {0, Side::SIX}
  };

  char choice;
  do {
    cout << "DICE ROLLING SIMULATION" << endl
         <<"===============================" << endl
        << "r. Roll Dice" << endl
        << "h. Display histogram" << endl
        << "q. Quit program\n" << endl

        << "\nEnter your choice:" << endl;

    // Reading a single character using the scanner
    cin >> choice;

    switch(choice) {
    case 'r': case 'R':
      for (Bar& b : histogram) {
        b.value = 0;
      }
      rollDice(histogram, 100);
      break;
    case 'h': case 'H':
      cout << getHistogram(histogram, '*') << endl;
      break;
    case 'q': case 'Q':
      cout << "Good bye\n" << endl;
      break;
    default:
      cout << "Invalid choice\n" << endl;
    }
  } while(choice != 'q');
}